It should also be noted that the NSMB series has lost popularity even on the 3DS. On the DS, NSMB was a beast that outsold every other DS game even in it's first year and had monster legs throughout it's lifespan. Well right now, Pokemon, Mario Kart, and even Mario 3D Land have sold better then NSMB 2. Even the legs for NSMB 2 are weaker then Mario Kart 7, which is rather telling considering NSMB DS had much better legs then Mario Kart DS.
So it looks like the way Nintendo treated that series, has started to finally bite them. Yeah it's still over 7 million right now, but in comparison to how it performed on the DS, it's not as strong a brand anymore since series that were less popular on that system are more popular on the 3DS now.